US 2003/0117118 discloses a method and a circuit to provide an output pulse signal with a modulated pulse width with increased accuracy for small values of a digital input number which determines a duration of a width of a pulse of the output signal. The output pulse signal is used to control a switching power supply for a DC load. According to the reference, without taking measurements, a resolution of a location of transition of a leading part and a trailing part of the output signal period would be constant for all values of an input digital number. That is, the resolution is determined by a duration of a period of a modulation clock pulse signal. In that case, if the value of the digital number is small, a change thereof by a small amount will have much more effect by percentage than changing a large value of the digital number by the same amount. For several applications, such as for accurate control of a switching power supply, this may be unwanted. Therefore, the reference discloses, for small values of the digital number, to extend or not the width of a pulse of output signal periods by one or more modulation clock pulse periods. To achieve that, clock pulses of different clock signals are counted and counted numbers are divided by each other to provide a whole result and a remainder result to therewith determine the times on which the width of the output signal pulses must be changed or not.
The prior art method is complex, difficult and expensive to implement and, more important, it does not provide an increase of resolution for relatively large values of the digital input number.